1. Field of the Invention
The present invention is related to an autofocus actuator, and in particular to an autofocus actuator which can be used in a compact electronic device equipped with a camera such as a digital camera or portable telephone or the like.
2. Description of the Prior Art
In digital cameras and the like, an actuator which can move lenses in the optical axis direction by the interaction between a magnetic field due to a permanent magnet and a magnetic field generated by electric current flowing through a coil is used for the purpose of carrying out autofocus and zoom. One example of such an actuator 100 is shown in FIGS. 16 and 17 which was filed by the applicant of this application.
The autofocus actuator 100 is composed of: a holder 110 including a cylindrical portion 111 having one end to which a lens assembly 105 is attached; a coil 120 fixedly secured to the holder 110 so that it is positioned around the cylindrical portion 111; a yoke 130 including a plurality of permanent magnets 140 disposed in a spaced-apart confronting relationship with the coil 120; a pair of leaf springs 160U, 160L for supporting the holder 110 displaceably in an optical axis direction with the holder 110 being positioned in a radial direction thereof; a stopper 170 attached to the holder 110 for securing the upper leaf spring 160U between the holder 110 and the stopper 170 in a sandwich manner; a cover 180 and a base 185 which are used as a pair of support frames, respectively, and provided outside of the pair of leaf springs 160U, 160L along the optical axis direction and adapted to secure the leaf springs 160U, 160L between the opposite end surfaces of the yoke 130 and the cover 180 and the base 185, respectively, in a sandwich manner, and both of the cover 180 and the base 185 having openings respectively formed at least on the parts that correspond to the lens assembly 105 attached to the holder 110; and a plurality of protruding portions which protrude inwardly from the peripheral edge of the opening of the cover 180 for restricting displacement of the holder 110 to which the stopper 170 is attached.
In the autofocus actuator 100 described above, the lens unit 105 attached to the holder 110 is displaceable in the optical axis direction by the interaction between the magnetic field of the permanent magnets 140 and the magnetic field generated by electric current flowing through the coil 120 when the electric current is supplied to the coil 120.
As an example of the external dimensions of an autofocus actuator mounted in a portable telephone, the length is approximately 10 mm, the width is approximately 10 mm, and the thickness is approximately 5 mm.
However, in such an autofocus actuator 100, in the case where a portable telephone provided with the actuator 100 falls from a height where it was being used, the stopper 170 attached to the holder 110 abuts against the protruding portions 183 so that a shock is applied to the holder 110. This causes a problem such as deformation of the leaf springs 160U, 160L and separation of bonding surfaces between the individual components, and the like, so that the autofocus actuator 100 is damaged.